The invention relates to sound attenuation of fan jet engines and specifically to an improved sound attenuating engine plug structure.
The major source of low frequency noise is produced by the turbulent combustion process. The combustion noise is characterized by a broad-band noise peaked at approximately 600 hertz. Prior art devices for reducing this core noise include lining the nozzle wall and/or the engine plug surface with acoustic material. This method was not completely successful as the resonant cavities that are formed in the state of the art duct lining material do not have the required depth for resonance at the low frequencies encountered due to available space. The duct lining material is too expensive to increase in thickness to achieve the required low frequency.
There has not been a successful solution to the core noise problem until the emergence of the instant invention.